Organic resin non-crimped staple fiber

ABSTRACT

The present invention is intended to provide an organic resin non-crimped staple fiber that has notably few defects and that uniformly disperses in a dispersion medium, and that is preferred for use in wet-laid nonwoven fabrics or resin reinforcement in applications such as in industrial materials and daily commodities. The organic resin non-crimped staple fiber of the present invention has a fineness of 0.0001 to 0.6 decitex, a fiber length of 0.01 to 5.0 millimeters, a moisture content of 10 to 200 weight %, a cut-end coefficient of 1.00 to 1.40, and a coefficient of variation relative to fiber length (CV %) of 0.0 to 15.0%, the cut-end coefficient and the coefficient of variation relative to fiber length being defined as follows: (1) Cut-End Coefficient=b/a, wherein a is the fiber diameter of a single yarn of the non-crimped staple fiber, and b is the maximum diameter at the cut end; (2) Coefficient of Variation Relative to Fiber Length (CV %)=(standard deviation of fiber length)/(mean value of fiber length)×100(%), wherein the number of measured single yarns is 50 in (1) and (2). The foregoing object can be achieved with this configuration.

TECHNICAL FIELD

The present invention relates to an organic resin non-crimped staple fiber having uniform dispersibility in media.

BACKGROUND ART

Wet-laid nonwoven fabrics made from a raw material that is partially or fully a staple fiber (as a short fiber as it is also called) obtained from a wholly aromatic polyamide having desirable properties such as mechanical characteristics, electrical characteristics, heat resistance, flame-retardation, and dimensional stability, or from more cost advantageous polyester are used in applications such as in electrical insulation paper, and a cleaning web for copiers (see, for example, PTL 1). Such wet-laid nonwoven fabrics are also used in a wide range of applications, including industrial materials such as reinforcing materials for resin molded products, and daily commodities. The increasing demand for more flexible, thinner and denser nonwoven fabrics has created a demand to increase the fineness of organic resin stable fibers used for the wet-laid nonwoven fabrics. In order to make a thin and dense nonwoven fabric, the dispersibility of the stable fiber in a dispersion medium needs to be improved for the formation of the wet-laid nonwoven fabric. This requires further reducing the fiber length of the stable fiber.

However, the fibers become more likely to intertangle as they become finer and increase the aspect ratio (fiber length-to-fiber diameter ratio). A nonwoven fabric made with such fibers tends to involve fluff ball defects. Such defects can be circumvented by reducing the fiber length and keeping the aspect ratio small. While this can reduce the fluff ball defects due to intertangling of fibers, defects at the cut-end of the fibers cause the stable fibers to be entangled with each other and aggregate, with the result that the product (e.g., nonwoven fabric) becomes defective. Ultrafine fibers of 0.6 decitex or less can be cut into essentially any fiber length as short as less than 1 millimeter with a known guillotine cutter. Specifically, the aspect ratio can be reduced. However, for reasons related to the mechanism of the cutting equipment, the fibers cannot be adequately held during the cutting procedure, and easily produce cut-end defects (see, for example, PTL 2). Stable fibers with the cut-end defects become entangled with each other and aggregate, and cause defects in nonwoven fabrics or reinforcing materials, making the final product defective. Particularly, when an organic resin with high fiber strength is used, the very high friction that occurs between the resin and the metal when cutting the fiber may quickly make the cutter blade blunt. Fine stable fibers also tend to involve cut-end defects such as projecting ends, and an obliquely cut surface relative to the fiber axis. Currently, for technical reasons, no non-crimped stable fibers are available that use organic resins having few dispersion defects. On the other hand, inventions are known concerning uniform fibers with small distributions of fiber diameters and fiber lengths, and fiber paper that use a fiber characterized by the shapes of its projecting portions (see PTL 3, 4, and 5).

CITATION LIST Patent Literature PTL 1: JP-A-2011-232509 PTL 2: JP-A-2009-221611 PTL 3: JP-A-2007-092235 PTL 4: JP-A-2000-119989 PTL 5: JP-A-2001-295191 SUMMARY OF INVENTION Technical Problem

The present invention was made under these circumstances, and the invention is concerned with an organic resin non-crimped staple fiber (stable fiber) that uniformly disperses in a medium without causing aggregation defects.

Solution to Problem

The present inventors conducted intensive studies to solve the foregoing problems, and arrived at using the following configurations as a solution to the foregoing problems.

1. The present invention was completed on the basis of the finding that the defects can be reduced with an organic resin non-crimped staple fiber having a fineness of 0.0001 to 0.6 decitex, a fiber length of 0.01 to 5.0 millimeters, a moisture content of 10 to 200 weight %, a cut-end coefficient of 1.00 to 1.40, and a coefficient of variation relative to fiber length (CV %) of 0.0 to 15.0%, the cut-end coefficient and the coefficient of variation relative to fiber length being defined as follows:

Cut-End Coefficient=b/a,  (1)

wherein a is the fiber diameter of a single yarn of the non-crimped staple fiber, and b is the maximum diameter at the cut end;

Coefficient of Variation Relative to Fiber Length (CV %)=(standard deviation of fiber length)/(mean value of fiber length)×100(%),  (2)

wherein the number of measured single yarns is 50 in (1) and (2).

Preferably, the present invention has the following configurations.

2. The organic resin non-crimped staple fiber according to the 1 above, wherein the non-crimped staple fiber is a polyester non-crimped staple fiber, a wholly aromatic polyamide non-crimped staple fiber, or a polyolefin non-crimped staple fiber.

3. The organic resin non-crimped staple fiber according to the 1 or 2 above, wherein the non-crimped staple fiber is a polyethylene terephthalate non-crimped staple fiber, a polytrimethylene terephthalate non-crimped staple fiber, a polytetramethylene terephthalate non-crimped staple fiber, a polyethylene naphthalate non-crimped staple fiber, a polytrimethylene naphthalate non-crimped staple fiber, a polytetramethylene naphthalate non-crimped staple fiber, a meta-type wholly aromatic polyamide non-crimped staple fiber, a para-type wholly aromatic polyamide non-crimped staple fiber, a polyethylene non-crimped staple fiber, or a polypropylene non-crimped staple fiber.

4. The organic resin non-crimped staple fiber according to any one of the 1 to 3 above, characterized in that the non-crimped staple fiber is a conjugate fiber configured from two or more organic resins.

Advantageous Effects of Invention

The present invention enables uniformly dispersing a non-crimped staple fiber of organic resin in a dispersion medium, and reducing generation of an aggregated clump in using a non-crimped staple fiber for wet-laid nonwoven fabrics or staple fiber reinforced resins. The nonwoven fabric or other products made from such non-crimped staple fibers contain staple fibers uniformly dispersed therein. The product nonwoven fabric is thus free from defects such as microscopic nonuniform dispersion of staple fibers, and variation of basis weight and thickness, and can have desirable properties such as uniform breathability and liquid permeability. The final product produced by processing such nonwoven fabrics involves few defects, and can have physical properties with improved reliability (reliable product warranty). The yield of the interim product (e.g., nonwoven fabric, and resin molded body) also can improve. The present invention is thus also highly advantageous in terms of resource saving and economy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view at the cut end of an organic resin non-crimped staple fiber of the present invention.

REFERENCE NUMERAL IN DRAWINGS

-   -   a: Fiber diameter of a single yarn     -   b: Maximum width of the fiber at the cut-end (maximum diameter         when the cut-end has a circular or a substantially circular         shape)

DESCRIPTION OF EMBODIMENTS (Organic Resin Composition) (Polyester)

Embodiments of the present invention are described below in detail. First, use of polyester as a specific example of the organic resin of the present invention is described. For example, the polyester is any of polyesters of aromatic dicarboxylic acid and aliphatic diol, including, for example, polyalkylene terephthalates such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate (polytetramethylene terephthalate), and polyalkylene naphthalates such as polyethylene naphthalate, polytrimethylene naphthalate, and polybutylene naphthalate (polytetramethylene naphthalate). Other examples include polyesters obtained from alicyclic dicarboxylic acid and aliphatic diol such as polyalkylene cyclohexane dicarboxylate, polyesters obtained from aromatic dicarboxylic acid and alicyclic diol such as polycyclohexane dimethylene terephthalate, polyesters obtained from aliphatic dicarboxylic acid and aliphatic diol such as polyethylene succinate, polybutylene succinate, and polyethylene adipate, and polyesters obtained from polyhydroxycarboxylic acid such as polylactic acid, and polyhydroxybenzoic acid.

Other examples include copolymers and blends containing these polyester components in any proportions. According to the intended purpose, one or more dicarboxylic acid components may be copolymerized. Examples of such components include isophthalic acid, phthalic acid, alkali metal salts of 5-sulfoisophthalic acid, quaternary ammonium salts of 5-sulfoisophthalic acid, quaternary phosphonium salts of 5-sulfoisophthalic acid, succinic acid, adipic acid, suberic acid, sebacic acid, cyclohexane dicarboxylic acid, α,β-(4-carboxyphenoxy)ethane, 4,4-dicarboxyphenyl, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1, 4-cyclohexane dicarboxylic acid, and diester compounds of these organic groups of 1 to 10 carbon atoms. According to the intended purpose, one of more diol components may be copolymerized. Examples of such components include diethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexane dimethanol, 2,2-bis(p-β-hydroxyethylphenyl)propane, polyethylene glycol, poly(1,2-propylene)glycol, poly(trimethylene)glycol, and poly(tetramethylene)glycol. It is also possible to form a branch by copolymerizing one or more components selected from ω-hydroxyalkylcarboxylic acid, pentaerythritol, trimethylolpropane, trimellitic acid, and hydroxycarboxylic acids such as trimesic acid, or compounds with three or more carboxylic acid components or hydroxyl groups. The polyester also includes mixtures of these and other polyesters of different compositions.

(Wholly Aromatic Polyamide: Meta-Type Wholly Aromatic Polyamide)

The following describes use of wholly aromatic polyamide as a specific example of the organic resin forming the organic resin non-crimped staple fiber of the present invention. A meta-type wholly aromatic polyamide staple fiber is described as an exemplary embodiment of the wholly aromatic polyamide staple fiber. The meta-type wholly aromatic polyamide as a raw material of the meta-type wholly aromatic polyamide staple fiber used for the organic resin non-crimped staple fiber of the present invention is configured from a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid component, and may be copolymerized with other copolymer component, such as a para-type component, provided that it does not interfere with the objects of the present invention.

For mechanical characteristics and heat resistance, particularly preferred for use in the present invention are meta-type wholly aromatic polyamides that contain a m-phenylene isophthalamide unit as a primary component. The meta-type wholly aromatic polyamides configured from a m-phenylene isophthalamide unit preferably contain the m-phenylene isophthalamide unit in 90 mol % or more, more preferably 95 mol % or more, particularly preferably 100 mol % of the total repeating unit.

Examples of the meta-type aromatic diamine component as a raw material of the meta-type wholly aromatic polyamide include m-phenylenediamine, 3,3′-diaminodiphenyl ether, 3,3′-diaminodiphenylsulfone, 3,4′-diaminodiphenyl ether, 3,4′-diaminodiphenylsulfone, and derivatives thereof having a substituent such as halogen, C₁₋₃ alkyl, and C₁₋₃ alkoxy in one or two of the aromatic rings of these aromatic diamine compounds. Specific examples include 2,4-tolylenediamine, 2,6-tolylenediamine, 2,4-diaminochlorobenzene, and 2,6-diaminochlorobenzene. Particularly preferred are wholly aromatic diamine components containing only m-phenylenediamine, or 70 mol % or more of m-phenylenediamine as the meta-type aromatic diamine component.

Examples of the meta-type aromatic dicarboxylic acid component as a raw material of the meta-type wholly aromatic polyamide include meta-type aromatic dicarboxylic acid dihalides. Examples of the meta-type aromatic dicarboxylic acid dihalides include isophthalic acid dihalides such as isophthalic acid dichloride, isophthalic acid bromide, isophthalic acid diiodide, and derivatives thereof having a substituent such as halogen, C₁₋₃ alkyl, C₁₋₃ alkoxy in the aromatic rings, for example, such as 3-chloroisophthalic acid dichloride, and 3-methoxyisophthalic acid dichloride. Particularly preferred are wholly aromatic dicarboxylic acid dihalides that contain only isophthalic acid dichloride, or 70 mol % or more of isophthalic acid dichloride.

(Wholly Aromatic Polyamide: Copolymer Components of Meta-Type Wholly Aromatic Polyamide)

The following copolymer components may be used other than the foregoing meta-type aromatic diamine components and meta-type aromatic dicarboxylic acid components. Example of aromatic diamines as such copolymer components include benzene derivatives (such as p-phenylenediamine, 2,5-diaminochlorobenzene, 2,5-diaminobromobenzene, and aminoanisidine(2-amino-4-methoxyaniline)), 1,5-naphthylenediamine, 1,6-naphthylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylketone, 4,4′-diaminodiphenylamine, and 4,4′-diaminodiphenylmethane. Examples of aromatic dicarboxylic acid components as copolymer components include terephthalic acid dichloride, 1,4-naphthalene dicarboxylic acid dichloride, 2,6-naphthalene dicarboxylic acid dichloride, 4,4′-biphenyl dicarboxylic acid dichloride, and 4,4′-diphenyl ether dicarboxylic acid dichloride. These copolymer components are contained in preferably 20 mol % or less of the total dicarboxylic acid component of the meta-type wholly aromatic polyamide because the properties of the meta-type wholly aromatic polyamide tend to deteriorate when the copolymerization ratio of these copolymer components is too high. Particularly, the meta-type wholly aromatic polyamide is preferably a polyamide containing the m-phenylene isophthalamide unit in 90 mol % or more of the total repeating unit, particularly preferably poly m-phenylene isophthalamide.

(Wholly Aromatic Polyamide: Para-Wholly Aromatic Polyamide)

The following describes use of a para-type wholly aromatic polyamide staple fiber as an embodiment of the staple fiber made of wholly aromatic polyamide. Examples of the para-type wholly aromatic polyamide as a raw material of the para-type wholly aromatic polyamide staple fiber used as an example of the organic resin non-crimped staple fiber of the present invention include para-type wholly aromatic polyamides of polyparaphenylene terephthalamide or polyparaphenylene terephthalamide copolymerized with 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenylsulfone, 3,4′-diaminodiphenylsulfone, or 4,4′-diaminodiphenylsulfone, and para-type wholly aromatic polyamides copolymerized with small quantities of isophthalic acid or m-phenylenediamine. Preferred are copolyparaphenylene-3,4′-oxydiphenylene terephthalamide, and polyparaphenylene terephthalamide. More preferred is copolyparaphenylene-3,4′-oxydiphenylene terephthalamide, a wholly aromatic polyamide containing terephthalic acid as an acid component, and a mixed diamine component containing 40 mol % or more of p-phenylenediamine and 40 mol % or more of 3,4′-diaminodiphenyl ether.

Examples of the aromatic diamine component that can be used for the para-type wholly aromatic polyamide include p-phenylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, and derivatives thereof having a substituent such as halogen, C₁₋₃ alkyl, C₁₋₃ alkoxy in one or two of the aromatic rings of these aromatic diamine compounds. Specific examples include 2,5-tolylenediamine, 2,5-diaminochlorobenzene, and 2,5-diaminobromobenzene. Particularly preferred are wholly aromatic diamine components that contain only p-phenylenediamine, or 70 mol % or more of p-phenylenediamine as the para-type aromatic diamine component.

Examples of the para-type aromatic dicarboxylic acid component as a raw material of the para-type wholly aromatic polyamide include para-type aromatic dicarboxylic acid dihalides. Examples of the para-type aromatic dicarboxylic acid dihalides include terephthalic acid dihalides such as terephthalic acid dichloride, terephthalic acid bromide, and terephthalic acid diiodide, and derivatives thereof having a substituent such as halogen, C₁₋₃ alkyl, and C₁-3 alkoxy in the aromatic rings, for example, such as 3-chloroterephthalic acid dichloride, and 3-methoxyterephthalic acid dichloride. Particularly preferred are wholly aromatic dicarboxylic acid dihalides that contain only terephthalic acid dichloride, or 70 mol % or more of terephthalic acid dichloride.

(Wholly Aromatic Polyamide: Copolymer Components of Para-Type Wholly Aromatic Polyamide)

The following copolymer components may be used other than the foregoing para-type aromatic diamine components and para-type aromatic dicarboxylic acid components. Examples of aromatic diamines as such copolymer components include benzene derivatives (such as m-phenylenediamine, 2,4-diaminochlorobenzene, 2,6-diaminochlorobenzene, 2,4-diaminobromobenzene, 2,6-diaminobromobenzene, 2-amino-4-methoxyaniline, and 3-amino-4-methoxyaniline), 1,3-naphthylenediamine, 1,4-naphthylenediamine, 1,5-naphthylenediamine, 1,6-naphthylenediamine, 3,4′-diaminodiphenyl ether, 3,4′-diaminodiphenylketone, 3,4′-diaminodiphenylamine, and 3,4′-diaminodiphenylmethane. Examples of aromatic dicarboxylic acid components as copolymer components include isophthalic acid dichloride, 1,3-naphthalene dicarboxylic acid dichloride, 2,7-naphthalene dicarboxylic acid dichloride, 3,4′-biphenyl dicarboxylic acid dichloride, and 3,4′-diphenyl ether dicarboxylic acid dichloride. These copolymer components are contained in preferably 20 mol % or less of the total dicarboxylic acid component of the meta-type wholly aromatic polyamide because the properties of the meta-type wholly aromatic polyamide tend to deteriorate when the copolymerization ratio of these copolymer components is too high. In referring to the non-crimped staple fibers of the meta-type wholly aromatic polyamides, it is to be understood that the “meta-” or “m-” notation may be appropriately replaced with “para-” or “p-” in the wholly aromatic polyamides. Such wholly aromatic polyamides also fall within the scope of the invention of the organic resin non-crimped staple fiber according to the present invention.

(Polyolefin)

The following describes use of polyolefin as a specific example of the organic resin forming the non-crimped staple fiber of the present invention. Preferred examples of the polyolefin used as the organic resin in the present invention include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, low-density polyethylene, ethylene-propylene random copolymerization polyolefin, and polyethylene or polypropylene copolymerized with a third component by block copolymerization or graft copolymerization. Examples of the third component include vinyl acetate, vinyl chloride, styrene, methyl acrylate, ethyl acrylate, isopropyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, acrylic acid, methacrylic acid, maleic acid, maleic acid anhydride, vinyl chloride, vinylidene chloride, acrylonitrile, and acrylamide. Particularly preferred is at least one polyolefin selected from the group consisting of high-density polyethylene, an ethylene-propylene random copolymer, polyethylene block or graft copolymerized with maleic acid anhydride, and polypropylene block copolymerized with maleic acid anhydride. More than one polyolefin may be selected from these polyolefins, and used as a mixture.

Other than these organic resins, it is also possible to use organic resins such as polyamide (e.g., nylon-6, and nylon-6,6), polyoxymethylene, polyphenylene ether, polyphenylene sulfide, cellulose, polysulfone, polyethersulfone, polycarbonate, and polyallylate. These organic resins may be polyester compositions containing known additives, for example, such as pigments, dyes, flatting agents, stain-proofing agents, antimicrobial agents, deodorants, fluorescent bleach, antioxidants, fire retardants, stabilizers, UV absorbers, and lubricants. Taken together, the non-crimped staple fiber in the organic resin non-crimped staple fiber of the present invention is preferably any of organic resin non-crimped staple fibers selected from a polyester non-crimped staple fiber, a wholly aromatic polyamide non-crimped staple fiber, and a polyolefin non-crimped staple fiber. In the organic resin non-crimped staple fiber of the present invention, it is also preferable that the non-crimped staple fiber is any of organic resin non-crimped staple fibers selected from a polyethylene terephthalate non-crimped staple fiber, a polytrimethylene terephthalate non-crimped staple fiber, a polytetramethylene terephthalate non-crimped staple fiber, a polyethylene naphthalate non-crimped staple fiber, a polytrimethylene naphthalate non-crimped staple fiber, a polytetramethylene naphthalate non-crimped staple fiber, a meta-type wholly aromatic polyamide non-crimped staple fiber, a para-type wholly aromatic polyamide non-crimped staple fiber, a polyethylene non-crimped staple fiber, and a polypropylene non-crimped staple fiber.

(Cross Sectional Shape and Configuration of Non-Crimped Staple Fiber)

As an example of the shape of the transverse plane of the organic resin non-crimped staple fiber of the present invention, the fiber may be a solid fiber, a hollow fiber, or a conjugate fiber, provided that the transverse plane orthogonal to the fiber axial direction has a circular cross section at the circumference. The shape of the fiber transverse plane is not limited to a circular cross section, and may have an oval cross section, a multi-lobed cross section such as a cross section with 3 to 8 lobes, or a modified cross section such as a triangular to octangular polygonal cross section. As used herein, “fiber transverse plane” means a fiber cross section taken at right angle to the fiber axis. The fiber configuration is not limited to fibers of a single organic resin. The non-crimped staple fiber of the present invention may be a conjugate fiber configured from two or more organic resins. The conjugate fiber may have a form of, for example, a concentric sheath-core conjugate fiber, an eccentric sheath-core conjugate fiber, a side-by-side conjugate fiber, an island-in-the-sea conjugate fiber, and a segmented pie conjugate fiber.

With the conjugate fiber configuration, the organic resin non-crimped staple fiber of the present invention may be provided as, for example, a fine fiber of 0.01 dtex or less, or a binder fiber bonded to other fibers under heat and pressure.

Specific examples of the polyester-containing conjugate fiber include sheath-core conjugate fibers in which polyalkylene terephthalates such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, or polyalkylene naphthalates such as polyethylene naphthalate, polytrimethylene naphthalate, or polybutylene naphthalate are disposed as the core component, and a copolymerized polyester or polyolefin is disposed as the sheath component. The conjugate fiber also may be, for example, an island-in-the-sea conjugate fiber in which a core component organic resin such as above is disposed as the island component, and a sheath component organic resin such as above is disposed as the sea component. The conjugate fiber also may be, for example, a side-by-side conjugate fiber or a segmented pie conjugate fiber in which a core component organic resin such as above, and a sheath component organic resin such as above are separately disposed. Examples of the copolymer components of the copolymerized polyester include one or more of the compounds, for example, isophthalic acid, and polyethylene glycol, that can be copolymerized with the polyester components above.

The polyolefin-containing conjugate fiber may be, for example, a sheath-core conjugate fiber in which polypropylene (may be any of the polypropylenes above) is disposed as the core component, and polyethylene (may be any of the polyethylenes above), a randomly copolymerized polyolefin of ethylene and propylene, or copolymer polyethylene of polyethylene or polypropylene copolymerized with a third component by block or graft copolymerization is disposed as the sheath component. The polyolefin-containing conjugate fiber also may be, for example, an island-in-the-sea conjugate fiber in which an organic resin such as the core components above is disposed as the island component, and an organic resin such as the sheath components above is disposed as the sea component. The polyolefin-containing conjugate fiber also may be, for example, a side-by-side conjugate fiber or a segmented pie conjugate fiber in which a core component organic resin such as above, and a sheath component organic resin such as above are separately disposed.

The non-crimped staple fiber of the present invention may be an undrawn staple fiber or a drawn staple fiber. An undrawn staple fiber is preferable for use as a binder fiber, which is bonded to other fibers under heat and pressure using a calendar roller or the like.

(Fineness, Fiber Length, and Crimp of Non-Crimped Staple Fiber)

The organic resin non-crimped ultrafine staple fiber of the present invention has a single yarn fineness of 0.0001 to 0.6 decitex, preferably 0.007 to 0.55 decitex, more preferably 0.01 to 0.53 decitex. With a single yarn fineness of less than 0.0001 decitex, the staple fibers tend to seriously intertangle, and a nonwoven fabric made from the non-crimped staple fiber of the present invention may have a defective texture. Small single yarn finenesses also cause difficulties in yarn making. Specifically, small finenesses are not preferable as they cause breaking of yarn or fluffing during yarn making, which makes it difficult to stably produce fibers of desirable quality, and increases the cost of the staple fiber. Another disadvantage of small single yarn finenesses is that the increased contact area between the cutter and the fiber increases the discharge resistance due to the fiber-metal friction when cutting the fiber, and cause the blade to easily break, or wear at the blade edge. However, an ultrafine non-crimped staple fiber with a fineness as small as 0.0002 to 0.006 decitex, despite the small single yarn fineness, has desirable properties such as moisture permeability and waterproofing, odor adsorption, and the efficiency for trapping microscopic objects, and can provide desirable effects different from the effects of the staple fibers of the foregoing fineness ranges, for example, in applications such as abrasive cloths for magnetic discs, and separator or capacitor papers for batteries. Staple fibers with such small finesses thus also represent a preferred form of the present invention. On the other hand, with a single yarn fineness exceeding 0.6 decitex, it becomes difficult to exploit the advantages of the ultrafine fiber, specifically the high nonwoven fabric strength, the high paper strength, and the high density of the nonwoven fabric or the like in a low basis weight region.

The organic resin non-crimped staple fiber of the present invention has a fiber length of 0.01 to 5.0 millimeters, preferably 0.015 to 4.0 millimeters, more preferably 0.02 to 3.5 millimeters, further preferably 1.0 to 3.3 millimeters. When the fiber length exceeds 5.0 millimeters, the fibers tend to intertangle, and cause defects. With a fiber length of less than 0.01 millimeters, the aspect ratio as a ratio of fiber length to the width or the oblong diameter of the fiber transverse plane becomes too small. This is not preferable in terms of fiber binding in a nonwoven fabric, and the strength of a nonwoven fabric. A fiber length may be selected according to such factors as the intended use, and processability. A staple fiber with the foregoing ultrafine finenesses and a fiber length of 0.015 to 0.06 mm can be as effective as the ultrafine staple fiber despite the stable fiber length, and such staple fibers also represent a preferred form of the present invention.

The staple fiber of the present invention needs to be non-crimped, and there is no need to actively impart crimps. When crimped, the staple fiber may not uniformly disperse upon being dispersed in a dispersion medium, or a nonwoven fabric produced from such staple fibers may not be able to have a low basis weight.

(Cut-End Coefficient of Non-Crimped Staple Fiber)

The organic resin non-crimped staple fiber of the present invention needs to have a cut-end coefficient of 1.00 to 1.40. The cut-end coefficient represents the extent of cut-end defect as defined in the present invention. The cut-end coefficient is described below in detail with reference to FIG. 1, which schematically represents an end portion of the non-crimped staple fiber of the present invention. Referring to FIG. 1, the cut-end coefficient is represented by b/a, where b is the maximum width along a direction orthogonal to the fiber axis at the cut end portion (or the maximum diameter when the cut end shape is circular or substantially circular), and a is the thickness of a single yarn (or the fiber diameter or fiber width of a single yarn) on the side surface at the cut end of the non-crimped staple fiber magnified with a light microscope. The cut-end coefficient is a measure of the spread of the shape of the staple fiber at the cut end portion relative to a normal single yarn thickness, and can be used as an index of the appropriateness of the shape at the cut end portion. A staple fiber with an index above 1.00 crushes under the pressure exerted right angle to the fiber axis when cutting the fiber, and has a large wide shape at the end. Such a wide shape is not a simple expansion of the shape of the fiber transverse plane, but can be described as a shape with no point symmetry. Specifically, the large wide shape is often different from the shape of the fiber transverse plane, and does not usually have a circular cross section when the fiber transverse plane has a circular cross section. The large wide shape also does not usually reflect the modified cross section of the fiber transverse plane when the transverse plane cross section is irregular in shape. When the cut-end coefficient as an index of the fiber shape is 1.00 to 1.40, the fiber can uniformly disperse in a dispersion medium, and generation of aggregated clumps can be reduced even when the cut-end has a shape different from the shape of the fiber transverse plane itself of the single yarn fiber. The effects of the present invention still can be obtained in this case. However, an index above 1.40 makes the shape defective by making the maximum width b of the large wide shape excessively large. A staple fiber with such a defective cut-end shape has a terminal projection, and becomes entangled with other staple fibers when dispersed in a dispersion medium. Such tangles serve as the trapping points of staple fibers having normal cut-ends, and often cause undispersed clumps in the staple fibers in the dispersion medium. The undispersed clumps lead to defective appearance or performance in a nonwoven fabric or other such products produced with the non-crimped staple fiber of the present invention. The proportion of fibers with defective cut-ends thus needs to be reduced below certain levels to reduce such defects. Studies by the present inventors revealed that the defects can be reduced when the cut-end coefficient ranges from 1.00 to 1.40, and that a cut-end coefficient above 1.40 creates a cut-end projection, or a shape that causes tangles. The present invention was completed on the basis of these findings. A cut-end coefficient of 1.00 means that the shape of the cut-end portion of the staple fiber and the shape of the fiber transverse plane completely match in all non-crimped staple fibers. The cut-end coefficient cannot take values below 1.0 with cutting methods that are generally considered practicable. The cut-end coefficient was measured by observing the side surface at the cut-end of randomly collected 50 non-crimped staple fibers with a light microscope or a scanning electron microscope, using the length measurement functionality of the microscope. The results were averaged for evaluation. The fibers show desirable medium dispersibility with no aggregated clumps when the cut-end coefficient is 1.00 to 1.40, preferably 1.001 to 1.35, further preferably 1.01 to 1.30. The most desirable state is when the cut-end coefficient is 1.00, as mentioned above.

(Variation of Fiber Length of Non-Crimped Staple Fiber)

Fiber length variation needs to be reduced in the non-crimped staple fiber of the present invention. Desirably, the coefficient of variation relative to fiber length (the percentage of the standard deviation relative to mean value) is 0.0% to 15.0%, preferably 0.01% to 14.0%, more preferably 0.1% to 13.0% in a fiber length measurement of randomly selected 50 non-crimped staple fibers. With a large fiber length variation, fibers with large aspect ratios (fiber length/fiber diameter) generate, and the fibers become more likely to contact and become entangled with each other upon being stirred in a dispersion medium. It is important to reduce fiber length variation because this becomes more likely as the fineness (fiber diameter) decreases. For the measurement of coefficient of variation relative to fiber length, randomly selected 50 staple fiber samples are placed on a cover glass, and magnified with a light microscope or a scanning electron microscope under the weight on the cover glass. The fiber lengths are then measured in the magnified image using the length measurement functionality of the light microscope or scanning electron microscope, and the mean value and the standard deviation are calculated. The ratio of standard deviation to mean value is then calculated to determine the coefficient of variation relative to fiber length. The non-crimped staple fiber of the present invention is preferably a drawn yarn. With a drawn yarn, a wet-laid nonwoven fabric or other such products made from the non-crimped staple fiber of the present invention can have a sufficient tensile strength, or other strengths necessary as a nonwoven fabric.

(Moisture Content of Non-Crimped Staple Fiber)

The non-crimped staple fiber of the present invention needs to have a moisture content of 10 to 200 weight %. A moisture content of less than 10 weight % is not preferable because it makes it difficult for the staple fibers to form a bundle, and tends to increase the cut-end coefficient or the variation coefficient of fiber length. On the other hand, a moisture content above 200 weight % is not preferable because it causes a large amount of water to become removed from the fiber tow, and may interfere with the ease of handling of the fiber bundle in the cutting process. Preferably, moisture is imparted before the cutting process in staple fiber production. The moisture content can be adjusted by imparting water with an oiling roller when the desired moisture content is toward the lower end of the foregoing range, or with nip rollers by which the fibers dipped in water are held and squeezed when the desired moisture content is toward the upper end of the foregoing range. When even smaller moisture contents are needed, water may be imparted by spraying. When spraying water, water may be imparted after the cutting process. The moisture content is preferably 12 to 150 weight %, more preferably 13 to 120 weight %, further preferably 16 to 100 weight %.

(Producing Process of Organic Resin Non-Crimped Staple Fiber)

The organic resin non-crimped staple fiber of the present invention above may be produced by using, for example, the following processes.

(Producing Process of Polyester Non-Crimped Staple Fiber)

A process for producing the polyester non-crimped staple fiber is described first. A polyester polymer is melted, ejected through a spinneret of known spinning equipment, and taken up at a rate of 100 to 2000 m/min while being cooled with cooled air to obtain an undrawn yarn. The undrawn yarn is drawn in 70 to 100° C. hot water or in a 100 to 125° C. steam, and an oil is imparted to obtain a drawn yarn. The drawn yarn is then subjected to drying, and, as required, a relaxation heat treatment to obtain a fiber bundle, which is then cut into a fiber length of 0.01 to 5.0 millimeters to obtain a non-crimped staple fiber.

Preferably, water is imparted to the fiber bundle before cutting the fiber bundle, as described above. The method of imparting water to the fiber bundle is not particularly limited, and water may be imparted by using, for example, a spray method, an oiling roller method, or a dipping method, after the relaxation heat treatment and before feeding the fiber bundle to the cutter. The oiling roller method is preferred in terms of uniformly imparting moisture in the foregoing ranges. When using a spray method or an oiling roller method, water should be imparted from the both sides of the fiber bundle to uniformly impart water to the fiber bundle.

The method for cutting the fiber bundle into a predetermined fiber length is not particularly limited. However, when a guillotine fiber-bundle cutter device is used to cut fibers of fine single yarns, the fibers easily bend or buckle, and the cutting blade may not contact the fibers at right angle, producing obliquely cut fibers, or fibers of different lengths. Such nonuniformity is believed to be due to the cutting method of the guillotine fiber-bundle cutter device, whereby a fiber bundle is pushed for the predetermined cut length toward the shear blades composed of a fixed blade and a movable blade. This may not be desirable as it increases the cut-end coefficient or the coefficient of variation relative to fiber length (fiber length variation) of the present invention.

When using a guillotine fiber-bundle cutter device, movement of the fiber bundle should thus be restricted while cutting the fibers so that the fiber bundle does not bend or buckle under its weight or under the pressure of the cutter blade. Typically, fiber bundles are restricted by being wrapped in a sheet-like material. It is, however, not always possible to sufficiently restrict movement of the fiber bundle with a method that wraps the fiber bundle in, for example, paper. In a more preferred method, the fiber bundle is dipped in water, and frozen after being degassed to make an ice pillar and fix the fiber bundle. The fiber bundle is then cut in the ice pillar with a guillotine cutter, and the ice (water) is removed. This method involves less fiber displacement, and makes the coefficient of variation relative to fiber length (fiber length variation) desirable to prevent the cut-end defect. The ice pillar may be replaced by a dry ice pillar.

Another method to cut a fiber bundle into a predetermined length uses an Eastman or other such rotary cutters with multiple cutter blades that are radially disposed outwardly at regular intervals. In this method, a fiber bundle is rolled onto the rotary cutter blades, and is continuously cut into a predetermined length while being pressed against the cutting blades. This cutting method has limitations in the cutter blade intervals with which the cut non-crimped staple fibers can be discharged. The method is nonetheless preferable because of the advantage that the cut-end defect or the fiber length variation due to single yarn displacement can be reduced by applying a moderate tension to the fiber bundle with the constituent single yarns being uniformly aligned without a slack before feeding the fiber bundle to the rotary cutter device. However, the method involves problems intrinsic to the device structure, including the large discharge resistance of the cut fibers, and breaking of the cutter blade. The discharge resistance can be reduced by providing a large space for the cut fibers in the device structure, whereas breaking of the cutter blade can be prevented by reducing the fiber-metal friction with a diamond-like coating applied to the cutter blade surface. In this way, a fiber with the desired fiber length of 5.0 millimeters or less, or a shorter fiber of a 3.0 millimeters or less can be stably obtained.

The rotary cutter device typically includes cutter blades, and feed rollers for supplying a fiber bundle to the cutter blade. Desirably, the draft rate of the rotary cutter and the feed rollers [(circumferential velocity of rotary cutter)/(circumferential velocity of feed rollers)] is set to 1.01 to 1.05. With a draft rate of less than 1.01, the tension created in the single yarn fibers of the fiber bundle tends to vary when cutting long fibers, and variation often occurs in the fiber length of the resulting staple fibers. A draft rate above 1.05 is not preferable because it has the possibility of mechanically stretching the fiber itself, and altering the physical properties of the fiber. Specifically, when using a rotary cutter device, a staple fiber with a coefficient of variation relative to fiber length of 0.0 to 15.0% can be obtained by setting the draft ratio as above. Desirably, the fiber bundle is cut by being pressed with pressure rollers installed at a certain clearance between the rollers and the edge of the cutter blade of the rotary cutter. By being cut under the gradually applied pressure of the pressure rollers, the cut fibers experience less resistance as they pass between the cutter blades, and can have less deformation at the cut-end. Further, with the pressure applied to the edge of the cutter blade at a certain clearance between the rollers and the edge, the amount of the fiber bundle rolled onto the rotary cutter can remain constant during a continuous operation. The fiber bundle at the outermost periphery becomes relaxed in fiber direction as it approaches the rotor center, and is cut upon contacting the cutter blade. Here, any fluctuation in the roll amount of the fiber bundle leads to variation of the extent of relaxation, and varies the fiber length.

(Producing Process of Meta-Type Wholly Aromatic Polyamide Non-Crimped Staple Fiber)

The following describes a process for producing the wholly aromatic polyamide non-crimped staple fiber. The process will be described through the case of a meta-type wholly aromatic polyamide staple fiber as a specific example of the wholly aromatic polyamide staple fiber of the present invention. The process is described in steps, which include a meta-type wholly aromatic polyamide producing step, a spinning solution preparation step, a spinning and coagulation step, a plasticization draw bath drawing step, a washing step, a saturated water vapor treatment step, a dry heat treatment step, and a cutting step.

[Meta-Type Wholly Aromatic Polyamide Producing Step]

The meta-type wholly aromatic polyamide producing process is not particularly limited, and processes such as solution polymerization and interface polymerization may be used that use, for example, a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid dichloride component as raw materials. For example, m-phenylenediamine and isophthalic acid dichloride may be used as raw materials. The degree of polymerization of the meta-type wholly aromatic polyamide should be 1.3 to 3.0 dL/g in terms of an inherent viscosity (IV) as measured by using 30° C. concentrated sulfuric acid as solvent.

[Spinning Solution Preparation Step]

A typical example of the producing process of the meta-type wholly aromatic polyamide non-crimped staple fiber used in the present invention is described below. First, a long fiber is produced in the steps described below. The long fiber is then fed to the cutting step to obtain the meta-type wholly aromatic polyamide staple fiber.

In the spinning solution preparation step, the meta-type wholly aromatic polyamide is dissolved in an amide solvent to prepare a spinning solution (meta-type wholly aromatic polyamide polymer solution). The spinning solution is typically prepared with an amide solvent. Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetoamide (DMAc). Preferred for solubility and safety of handling are NMP and DMAc. The concentration of the spinning solution may be appropriately selected taking into consideration the coagulation rate, and the solubility of the meta-type wholly aromatic polyamide in the next spinning and coagulation step. Typically, the concentration is preferably, for example, 10 to 30 mass % when the meta-type wholly aromatic polyamide is poly m-phenylene isophthalamide, and the solvent is NMP.

[Spinning and Coagulation Step]

In the spinning and coagulation step, the spinning solution (meta-type wholly aromatic polyamide polymer solution) obtained above is spun into a coagulation solution to coagulate, and a porous fiber material is obtained. The spinning device is not particularly limited, and a known wet spinning device may be used. Conditions such as the number of spinning holes in the spinneret, the hole arrangement, and the hole shape are not particularly limited, as long as the solution can be stably wet spun. For example, a multi-hole spinneret for staple fibers (short fibers) with 500 to 30,000 holes, and a spinning hole diameter of 0.05 to 0.2 millimeters may be used. The temperature of the spinning solution (meta-type wholly aromatic polyamide polymer solution) spun out of the spinneret should be 10 to 90° C. The coagulation bath is configured as a two-component aqueous solution of substantially amide solvent and water. The amide solvent in the coagulation bath composition is not particularly limited, as long as it can dissolve the meta-type wholly aromatic polyamide, and is desirably miscible with water. Preferred examples include N-methyl-2-pyrrolidone, dimethylacetoamide, dimethylformamide, and dimethylimidazolidinone (e.g., 1,3-dimethyl-2-imidazolidinone). The mixing ratio (weight ratio) of the amide solvent to water is preferably 10/90 to 90/10, more preferably 30/70 to 70/30.

As required, an inorganic sodium salt, a potassium salt, a magnesium salt, or a calcium salt may be dissolved in the coagulation bath in 0.1 to 8.0 weight %.

[Plasticization Draw Bath Drawing Step]

In the plasticization draw bath drawing step, the fiber bundle is drawn in a plasticization draw bath while the porous fiber (yarn) bundle obtained after the coagulation in the coagulation bath is in a plastic state. The plasticization draw bath used to obtain the fiber used in the present invention is prepared from an aqueous solution containing an amide solvent, and is substantially salt free. The amide solvent is not particularly limited, as long as it can swell the meta-type wholly aromatic polyamide, and is desirably miscible with water. Examples of the amide solvent include N-methyl-2-pyrrolidone, dimethylacetoamide, dimethylformamide, and dimethylimidazolidinone.

The temperature and the composition of the plasticization draw bath are closely related to each other. Preferably, the plasticization draw bath contains 20 to 70 mass % of the amide solvent, and has a temperature of 20 to 70° C. When the mass concentration of the amide solvent, or the temperature is below these ranges, the porous fiber material does not sufficiently plasticize, and it becomes difficult to ensure a sufficient draw ratio in the plasticization drawing.

On the other hand, when the mass concentration of the amide solvent, or the temperature is above the foregoing ranges, the porous fiber surface melts and fuses, and makes it difficult to desirably make yarns.

In obtaining the fiber used in the present invention, the draw ratio in the plasticization draw bath is preferably 1.5 to 10, more preferably 2.0 to 6.0. With a draw ratio of less than 1.5, the resulting fiber suffers from poor mechanical characteristics (e.g., strength, and modulus), and it may become difficult to provide the necessary break strength for the nonwoven fabric or other such products produced with the fiber of the present invention. It also becomes difficult to promote sufficient removal of the solvent from the porous fiber material, making it difficult to produce a fiber with 1.0 mass % or less of residual solvent.

[Washing Step]

In the washing step, the fiber from the plasticization draw bath drawing step is sufficiently washed with water. Preferably, washing is performed in stages to avoid adverse effects on fiber quality. Particularly, the temperature of the washing bath, and the concentration of the amide solvent in the washing bath in the washing step have effects on the state of the amide solvent extracted from the fiber, and the state of water entering the fiber from the washing bath. In order to optimize these states, it is preferable to perform the washing step in stages, and control the temperature condition, and the concentration condition of the amide solvent.

[Saturated Water Vapor Treatment Step]

In the saturated water vapor treatment step, the fiber washed in the washing step is subjected to a heat treatment in a saturated water vapor. The saturated water vapor treatment enables improving alignment while reducing fiber crystallization. The heat treatment in a saturated water vapor atmosphere allows the heat to more uniformly reach inside the fiber bundle than in a dry heat treatment, and enables producing a more uniform fiber. The draw ratio in the saturated water vapor treatment step is also closely related to development of fiber strength. Any draw ratio may be chosen, taking into account the required physical properties of the product. In the present invention, the draw ratio is 0.7 to 5.0, preferably 1.1 to 2.0. A draw ratio below 0.7 is not preferable as it lowers the cohesion of the fiber bundle (yarn) in a saturated water vapor atmosphere. On the other hand, a draw ratio above 5.0 is not preferable as it increases the occurrence of single yarn breakage during the draw, and generates a fluff or broken yarns. Preferably, the saturated water vapor treatment is performed for 0.5 to 5.0 seconds. When continuously treating the running fiber bundle, the most effective treatment time should be selected by appropriately adjusting factors that determine the treatment time, specifically the running distance and the running speed of the fiber bundle in a water vapor treatment vessel.

[Dry Heat Treatment Step]

In the dry heat treatment step, the fiber from the saturated water vapor treatment step is subjected to a dry heat treatment. The dry heat treatment method is not particularly limited, and may be, for example, a method that uses a hot plate, a heat roller, or the like. After the dry heat treatment, a long fiber of meta-type wholly aromatic polyamide can be finally obtained. The heat treatment temperature of the dry heat treatment step preferably ranges from 250 to 400° C., more preferably 300 to 380° C. When the dry heat treatment temperature is less than 250° C., the porous fiber cannot be sufficiently densified, and the mechanical characteristics of the fiber become insufficient. On the other hand, a dry heat treatment temperature above 400° C. is not preferable because it causes heat deterioration on fiber surface, and lowers quality.

The draw ratio in the dry heat treatment step is closely related to development of fiber strength. Any draw ratio may be chosen according to the strength or other required properties of the fiber. The draw ratio in the dry heat treatment step is preferably 0.7 to 4.0, more preferably 1.5 to 3.0. When the draw ratio is less than 0.7, the step tension decreases, and the fiber suffers from poor mechanical characteristics. On the other hand, when the draw ratio is above 4.0, the single yarn becomes more likely to break while being drawn, and generates a fluff or broken yarns. As used herein, “draw ratio” is the ratio of the treated fiber length to the undrawn fiber length, as with the case of the draw rate described in conjunction with the saturated water vapor treatment step. For example, a draw ratio of 0.7 means that the fiber becomes 70% of the original length after it restrictively shrinks in the dry heat treatment step. A draw ratio of 1.0 means a fixed-length heat treatment. The process time of the dry heat treatment step is preferably 1.0 to 45 seconds. The treatment time may be adjusted according to the running speed of the fiber bundle, and the contact length with a hot plate, a heat roller, or the like.

[Cutting Step]

In the production of the wholly aromatic polyamide non-crimped staple fiber of the present invention, the meta-type wholly aromatic polyamide long fiber after the dry heat treatment is cut into a predetermined length in a cutting step. The method used to cut the fiber into a predetermined length is not particularly limited. However, considerations need to be given with regard to use of a guillotine fiber-bundle cutter device that includes shear blades composed of a fixed blade and a movable blade, and in which a fiber bundle is pushed for a predetermined cut length toward the shear blades. Specifically, when cutting fibers of fine single yarns, the fibers easily bend or buckle, and the cutting blade may not contact the fibers at right angle, producing obliquely cut fibers, or fibers of different lengths. This may not be appropriate as it increases the cut-end coefficient, or the coefficient of variation relative to fiber length (fiber length variation) of the present invention. By performing the cutting procedure in the same manner as in the production of the polyester non-crimped staple fiber with care being given to the considerations described therein, a staple fiber of predetermined physical properties can be obtained also for the meta-type wholly aromatic polyamide non-crimped fiber.

In the steps from the meta-type wholly aromatic polyamide producing step to the cutting step, it is to be understood that the “meta-” or “m-” notation may be appropriately replaced with “para-” or “p-”, and that the foregoing steps also represent the process for producing the organic resin non-crimped staple fiber of the present invention made from such corresponding para-type wholly aromatic polyamides.

(Producing Process of Polyolefin Non-Crimped Staple Fiber)

A process for producing the polyolefin non-crimped staple fiber is described below. In the polyolefin non-crimped staple fiber producing process, the polyester used as the organic resin in the polyester non-crimped staple fiber producing process is replaced with a desired polyolefin. The desired polyolefin non-crimped staple fiber can be produced by melt-spinning the selected polyolefin under the common melt-spinning conditions after replacing some of or all of these conditions with the conditions used in the polyester non-crimped staple fiber producing process above.

(Moisture Content in Cutting Step, and Effects of the Invention)

The moisture content of the fiber bundle fed to the rotary cutter is desirably 10 to 200% in the non-crimped staple fiber of any organic resin, whether it is a polyester, a wholly aromatic polyamide, or a polyolefin, as described above. The fibers in a fiber bundle with a moisture content of 10% or more bind together, and the fiber bundle uniformly contacts the cutter blade at right angle when being cut. The fibers thus contact the cutter blade under uniform pressure while being cut. This improves the cut-end coefficient, and the coefficient of variation relative to fiber length. The resulting staple fibers with the desirable cut-end coefficient and the desirable coefficient of variation relative to fiber length are thus less likely to include fibers of large aspect ratios. The fibers are thus less likely to be entangled with each other, and can uniformly disperse in a medium without causing aggregation defects. On the other hand, a moisture content above 200% causes a large amount of water to become removed from the tow, or the fibers in a fiber bundle state, and may interfere with the ease of handling. The moisture content should therefore be at most 200%. By confining the moisture content of the fiber bundle in the fiber cutting step in the foregoing range, the moisture content of the product organic resin non-crimped staple fiber can also fall in the foregoing range. The surface of the organic resin non-crimped staple fiber may be treated with a surface treatment agent such as a dispersant, a lightfast agent, a smoothing agent, an adhesive, or a mixture of these, provided that such a surface treatment is not detrimental to the effects of the present invention. When the non-crimped staple fiber is a polyester non-crimped staple fiber or a polyolefin non-crimped staple fiber, it is preferable to impart a polyester-polyether copolymer that is compatible with both the organic resin and the dispersion medium.

INDUSTRIAL APPLICABILITY

The organic resin non-crimped staple fiber of the present invention can uniformly disperse in a dispersion medium, and can reduce generation of aggregated clumps in applications such as wet-laid nonwoven fabrics, and staple fiber reinforced resins. The staple fibers in a nonwoven fabric or other such products made from the non-crimped staple fiber are also uniformly dispersed. The product nonwoven fabric is thus free from defects such as microscopic nonuniform dispersion of staple fibers, and variation of basis weight and thickness, and can have desirable properties such as uniform breathability and liquid permeability. The final product produced by processing such nonwoven fabrics involves few defects, and can have physical properties with improved reliability (reliable product warranty). The yield of the interim product (e.g., nonwoven fabric, and resin molded body) also can improve. The present invention is thus also highly advantageous in terms of resource saving and economy.

EXAMPLES

The following describes the configurations and the effects of the present invention in detail using Examples. The present invention, however, is in no way limited by the following Examples. In the following, “part” means “weight part”, unless otherwise stated. The values of various physical properties in Examples and Comparative Examples were measured according to the following methods.

(1) Inherent Viscosity: [η]

For the polyester fiber, 0.12 g of a fiber (polymer) sample was dissolved in 10 mL of a tetrachloroethane/phenol mixed solvent (volume ratio 1/1), and measured for inherent viscosity (dL/g) at 35° C. For the wholly aromatic polyamide fiber, the fiber (polymer) was dissolved in 97 mass % concentrated sulfuric acid, and measured for inherent viscosity (dL/g) at 30° C. with an Ostwald viscometer.

(2) Melt Flow Rate: MFR

Melt flow rate was measured according to condition 4 of JIS K 7210 (measurement temperature 190° C., load 21.18N). The melt flow rate is a measured value of a polymer pellet sample immediately before melt-spinning.

(3) Melting Point: Tm

The TA Instruments product TA-2920 differential scanning calorimeter DSC was used. For the measurement, a polymer sample (10 mg) was heated from room temperature to 260° C. at 10° C./min in a nitrogen atmosphere. The melting point was defined as the peak temperature at the crystal melting endothermic peak.

(4) Single Yarn Fineness

Single yarn fineness was measured by using the method described in JIS L 1015:2005 8.5.1, method A. Specifically, the following measurement technique was used. A small amount of a fiber sample was combed parallel to each other with a metal comb, and put on flock paper placed on a cutting board. With a gauge plate pressed against the fiber sample being pulled straight with a moderate force, the fiber sample was cut into a 30-mm length with the blade of a safety razor or the like. The fibers were counted, and a set of 300 fibers was weighed to determine apparent fineness. The actual fineness was calculated from the apparent fineness and the separately measured equilibrium moisture content, using the following equation. The actual fineness was calculated five times, and the mean value was determined.

F=[(100+R0)/(100+Rc)]×D

F: Actual fineness

D: Apparent fineness

R0: Formal moisture content (%) (value specified by JIS L 0105 4.1)

Rc: Equilibrium moisture content (%)

(5) Cut-End Coefficient

Fifty non-crimped staple fibers were randomly picked up, and placed on a cover glass. The fibers were observed with a light microscope or a scanning electron microscope under the weight of the cover glass. The fibers were then measured for maximum diameter b at the cut-end, and fiber diameter a of a single yarn (see FIG. 1), using the length measurement functionality of the light microscope or scanning electron microscope. The cut-end coefficient was calculated as follows.

Cut-end coefficient=b/a

The mean value of the measured values of each fiber was used for the evaluation of cut-end coefficient.

(6) Coefficient of Variation Relative to Fiber Length

Fifty non-crimped staple fibers were randomly picked up, and placed on a cover glass. The fibers were observed with a light microscope or a scanning electron microscope under the weight of the cover glass. The fiber length was then measured using the length measurement functionality of the light microscope or scanning electron microscope. After determining the mean value and the standard deviation, the coefficient of variation relative to fiber length (CV %) was calculated as follows.

Coefficient of variation relative to fiber length(CV %)=(standard deviation of fiber length)/(mean value of fiber length)×100(%)

(7) Moisture Content

About 100 g of fibers with moisture were bone-dried in a 120° C. hot-air circulation drier. Moisture content was determined from the weight W0 of the sample before drying, and the weight W1 of the sample after drying, as follows.

Moisture content (%)=[(W0−W1)/W1]×100

(8) Water Dispersibility

The dispersibility of fibers in water was evaluated to determine the presence or absence of a fiber aggregation defect due to cut-end and fiber length. Soft water (500 cc) was placed in a 1000-cc beaker, and fibers (0.5 g) that had been cut into a predetermined fiber length were put in the beaker, and stirred with a magnetic stirrer (stirrer) at ordinary temperature for 20 min. The fibers were filtered through a 0.15 mm-mesh metal net, and the number of fiber clumps with a size of 1 mm² or more remaining on the metal net was counted. The results are represented as Good when the number of fiber clumps was 3 or less, Acceptable when 3 to 5 fiber clumps were observed, and Poor when there were 5 or more fiber clumps.

Example 1

A polyethylene terephthalate (PET) chip with an inherent viscosity of 0.64 dL/g containing 0.3 weight % of titanium dioxide was melted at 290° C., ejected through a spinneret having 3000 round holes at an ejection rate of 450 g/min, and taken up at a rate of 1320 m/min to obtain polyethylene terephthalate undrawn yarns having a single yarn fineness of 1.14 decitex. The undrawn yarns were aligned, and a tow of 140000 decitex was obtained. The tow was drawn in two stages in hot water at a total draw ratio of 2.51, and a polyester-polyether copolymer was imparted in 0.3 weight % of the polyester fiber weight. After imparting the polyester-polyether copolymer, the yarns were dried, and heat set at 120° C. in a relaxed state to obtain an uncrimped drawn polyethylene terephthalate fiber bundle having a single yarn fineness of 0.51 decitex. Water was imparted to the drawn polyethylene terephthalate fiber bundle with an oiling roller to make the moisture content 15%, and the fibers were cut into staple fibers with a fiber length of 3.0 millimeters, using an Eastman rotary cutter fiber cutting device with a blade interval of 3.0 millimeters. The fibers were cut with a draft rate of 1.02 between the rotary cutter and feed rollers under the pressure of a pressure roller pressing the fiber bundle against the cutter blade. Table 1 shows the evaluation results, including the fineness, the moisture content, the cut-end coefficient, the coefficient of variation relative to fiber length, and the water dispersibility of the polyester non-crimped staple fiber.

Example 2

The same procedures used in Example 1 were performed to obtain a non-crimped staple fiber, except that the fiber was cut into a staple fiber with a fiber length of 1.5 millimeters. The evaluation results for the polyester non-crimped staple fiber are presented in Table 1.

Example 3

The non-crimped drawn polyethylene terephthalate fiber bundle obtained in Example 1 was dipped in water, and held and squeezed with nip rollers to make the moisture content 30%. Four of the fiber bundles prepared in this fashion were disposed side by side to make a fiber bundle. The fiber bundle was dipped in a cylindrical container that had been charged with boiled processing water, and frozen at an atmospheric temperature of −12° C. over the course of 15 h to obtain a fiber bundle contained in ice. The fiber bundle in ice was then cut into a fiber length of 1.5 millimeters using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The polyester non-crimped staple fiber was evaluated after being thawed. The results are presented in Table 1. The notation “ice pillar+guillotine” used in Tables 1 and 3 refers to the fiber bundles of Examples 3 to 5 that were cut in ice with a guillotine cutter.

Example 4

An ultrafine long fiber bundle was produced from an island-in-the-sea conjugate fiber by using the following procedures. Polyethylene terephthalate with a melt viscosity of 120 Pa·sec at 285° C. was used as the island component. As the sea component, altered copolymerized polyethylene terephthalate with a 285° C. melt viscosity of 135 Pa·sec was used that was prepared by copolymerizing 4 weight % of polyethylene glycol having a number average molecular weight of 4000, and 9 mol % of 5-sodium sulfoisophthalic acid. The fiber was melt-spun at a spinning speed of 1500 m/min to obtain an ultrafine fiber precursor fiber (island-in-the-sea conjugate fiber) that was drawn 3.9 times, using a spinneret designed to produce a conjugate fiber containing 400 islands in a sea component:island component weight ratio of 30:70. The drawn ultrafine fiber precursor fibers were bundled together to obtain a fiber bundle of 500000 decitex, and dipped and passed through a 75° C., 4 weight % sodium hydroxide aqueous solution at such a rate that the fibers were in the solution for 15 min. This produced an ultrafine long fiber bundle (single yarn fiber diameter of 750 nanometers, 0.0056 decitex) that was 27.6 weight % less than the fiber bundle of the ultrafine fiber precursor fibers.

The ultrafine long fiber bundle was dipped in water, and held and squeezed with nip rollers to make the moisture content 100%. Four of the fiber bundles prepared in this fashion were disposed side by side to make a fiber bundle. The fiber bundle was dipped in a cylindrical container that had been charged with boiled processing water, and frozen at an atmospheric temperature of −12° C. over the course of 15 h to obtain a fiber bundle contained in ice. The fiber bundle in ice was then cut into a fiber length of 0.05 millimeters using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The polyester non-crimped staple fiber was evaluated after being thawed. The results are presented in Table 1.

Example 5

The same procedures used in Example 4 were performed, except that a spinneret designed to produce 1500 islands was used, and that the fibers were spun, drawn, and cut to produce a fiber bundle with a single yarn fineness of 0.0004 decitex (fiber diameter of 200 nanometers), and a fiber length of 0.02 millimeters. The evaluation results for the polyester non-crimped staple fiber are presented in Table 1.

TABLE 1 Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Fiber configuration — Single component Single component Single Component Island-in-sea conjugate Island-in-sea conjugate fiber fiber fiber fiber fiber Organic resin — PET PET PET Island component: PET, Island component: PET, Sea component: Sea component: Copolymerized PET Copolymerized PET Cutting method — Rotary cutter Rotary cutter Ice pillar + guillotine Ice pillar + guillotine Ice pillar + guillotine Fineness dtex 0.51 0.51 0.51 0.0056 0.0004 Fiber length mm 3.0 1.5 1.5 0.05 0.02 Moisture content weight % 15 15 30 100 100 Cut-end coefficient — 1.02 1.03 1.20 1.30 1.30 coefficient of variation % 2.4 3.3 8.0 10.0 12.0 relative to fiber length Water dispersibility — Good Good Good Good Good

Comparative Example 1

Ten of the non-crimped drawn polyethylene terephthalate fiber bundles obtained in Example 1 were bundled to obtain a fiber bundle of 1400000 decitex. The fiber bundle was then wrapped in paper. The wrapped fiber bundle was cut into a fiber length of 3.0 millimeters to obtain a non-crimped staple fiber, using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The evaluation results for the polyester non-crimped staple fiber are presented in Table 2.

Comparative Example 2

The same procedures used in Comparative Example 1 were performed to obtain a non-crimped staple fiber, except that the fiber bundle was cut into a staple fiber with a fiber length of 1.5 millimeters. The evaluation results for the polyester non-crimped staple fiber are presented in Table 2.

Comparative Example 3

The same procedures used in Comparative Example 1 were performed to obtain a non-crimped staple fiber, except that the draft rate between the rotary cutter and the feed rollers was set to 0.98. The evaluation results for the polyester non-crimped staple fiber are presented in Table 2.

TABLE 2 Unit Com. Ex. 1 Com. Ex. 2 Com. Ex. 3 Fiber configuration — Single component Single component Single component fiber fiber fiber Organic resin — PET PET PET Cutting method — Guillotine Guillotine Rotary cutter Fineness dtex 0.51 0.51 0.51 Fiber length mm 3.0 1.5 3.0 Moisture content weight % 15 15 15 Cut-end coefficient — 1.50 1.60 1.02 coefficient of variation % 50.0 80.0 18.0 relative to fiber length Water dispersibility — Poor Poor Acceptable

Example 6 Spinning Solution Preparation Step

A reaction vessel equipped with a thermometer, an agitator, and a raw material inlet was charged with 815 parts of N-methyl-2-pyrrolidone (hereinafter, “NMP”) that had been dehydrated with molecular sieves. Thereafter, 108 parts of m-phenylenediamine was dissolved into the NMP, and the mixture was cooled to 0° C. For reaction, 203 parts of isophthalic acid chloride that had been purified by distillation, and pulverized in a nitrogen atmosphere was added to the cooled m-phenylenediamine solution while being stirred. The reaction temperature increased to about 50° C., and the mixture was kept stirred at this temperature for 60 min. The reaction was further allowed for 60 min under the applied heat of 60° C.

After the reaction, calcium hydroxide (70 parts) was added to the polymer solution in fine powdery form, and dissolved for neutralization over the course of 60 min (first neutralization). Four parts of the remaining calcium hydroxide was dispersed in 83 parts of NMP to prepare a slurry, and the slurry (neutralizer) was added to the neutralized polymer solution while being stirred (second neutralization). The second neutralization was performed at 40 to 60° C. with stirring for about 60 min to prepare a polymer solution (spinning solution) in which the calcium hydroxide was completely dissolved.

The polymer solution (spinning solution) had a polymer concentration of 14 (in terms of weight parts of the polymer with respect to the total 100 weight parts of the polymer and the NMP), and the resultant poly m-phenylene isophthalamide polymer had an inherent viscosity (IV) of 2.37 dL/g. The polymer solution (spinning solution) had a calcium chloride concentration of 46.6 parts, and a water concentration of 15.1 parts with respect to 100 parts of the polymer.

[Spinning and Coagulation Step]

The spinning solution prepared in the spinning solution preparation step was ejected and spun into a 40° C. coagulation bath through a spinneret having 500 holes with a hole diameter of 0.07 millimeters. The coagulation solution had a composition with a water:NMP:calcium chloride mass ratio of 48:48:4, and was passed through the coagulation bath over a dip length (effective coagulation bath length) of 70 cm at a yarn rate of 5 m/min. The porous fiber material after the coagulation in the coagulation bath had a density of 0.71 g/cm³.

[Plasticization Draw Bath Drawing Step]

The fiber bundle was drawn in a plasticization draw bath at a draw ratio of 3.0. The plasticization draw bath had a composition with a water:NMP:calcium chloride mass ratio of 44:54:2, and a temperature of 40° C.

[Washing Step]

The plasticized and drawn fiber bundle was thoroughly washed first with 30° C. cold water, and then with 60° C. hot water. The cold water and the hot water were checked for sufficiently lowered levels of amide solvent concentration after the washing.

[Saturated Water Vapor Treatment Step]

The fibers were then subjected to a saturated water vapor heat treatment at a draw ratio of 1.1 in a container with the maintained saturated water vapor pressure of 0.05 MPa. The heat treatment was performed under adjusted conditions, for example, by adjusting the running distance and the running speed of the fiber bundle, so that the fiber bundle was treated with saturated water vapor for about 1.0 second.

[Dry Heat Treatment Step]

A dry heat treatment was performed at a draw ratio of 1.0 (constant length) on a hot plate with a surface temperature of 360° C. The resulting poly m-phenylene isophthalamide fiber was rolled.

[Physical Properties of Long Fiber]

The poly m-phenylene isophthalamide drawn fiber was sufficiently dense with a fineness of 0.8 decitex, a density of 1.33 g/cm³, a tensile strength of 3.68 cN/dtex, and an elongation of 42%. The fiber had desirable mechanical characteristics, and there was no variation in quality. There was also not observed any abnormal yarn.

[Cutting Step]

A fiber bundle was produced from the roll of the poly m-phenylene isophthalamide fiber after the dry heat treatment. Water was imparted to the fiber bundle to make the moisture content 15%. The fiber bundle was then cut into staple fibers with a fiber length of 3.0 millimeters, using an Eastman rotary cutter fiber cutting device with a blade interval of 3.0 millimeters. The fiber bundle was cut with a draft rate of 1.02 between the rotary cutter and feed rollers under the pressure of a pressure roller pressing the fiber bundle against the cutter blade. Table 3 shows the evaluation results, including the fineness, the moisture content, the cut-end coefficient, the coefficient of variation relative to fiber length, and the water dispersibility of the meta-type wholly aromatic polyamide non-crimped staple fiber.

Example 7

Four of the fiber bundles produced by imparting water to the poly m-phenylene isophthalamide fiber rolled after the dry heat treatment in the manner described in Example 6 were disposed side by side to produce a fiber bundle. The fiber bundle prepared from the four parallel fiber bundles was frozen at an atmospheric temperature of −12° C. for 15 hours while being dipped in a cylindrical container charged with boiled processing water to obtain a fiber bundle contained in ice. The fiber bundle in ice was cut into a fiber length of 1.0 millimeters using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The meta-type wholly aromatic polyamide non-crimped staple fiber was evaluated after being thawed. The results are presented in Table 1.

Example 8

The same procedures used in Example 7 were performed, except that the fiber bundle was cut into a staple fiber with a fiber length of 0.02 millimeters. The meta-type wholly aromatic polyamide non-crimped staple fiber was evaluated after being thawed. The results are presented in Table 3.

TABLE 3 Unit Ex. 6 Ex. 7 Ex. 8 Fiber configuration — Single component Single component Single component fiber fiber fiber Organic resin — meta-type Wholly meta-type Wholly meta-type Wholly aromatic polyamide aromatic polyamide aromatic polyamide Cutting method — Rotary cutter Ice pillar + Ice pillar + guillotine guillotine Fineness dtex 0.80 0.80 0.80 Fiber length mm 3.0 1.0 0.02 Moisture content weight % 15 15 15 Cut-end coefficient — 1.07 1.25 1.35 coefficient of variation % 3.3 10.0 15.0 relative to fiber length Water dispersibility — Good Good Good

Comparative Example 4

The fiber bundle produced by imparting water to the poly m-phenylene isophthalamide fiber rolled after the dry heat treatment in the manner described in Example 6 was cut into a fiber length of 3.0 millimeters to obtain a non-crimped staple fiber, using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The evaluation results for the meta-type wholly aromatic polyamide non-crimped staple fiber are presented in Table 4.

Comparative Example 5

The fiber bundle produced by imparting water to the poly m-phenylene isophthalamide fiber rolled after the dry heat treatment in the manner described in Example 6 was cut into a fiber length of 1.0 millimeters to obtain a non-crimped staple fiber, using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The evaluation results for the meta-type wholly aromatic polyamide non-crimped staple fiber are presented in Table 4.

Comparative Example 6

The same procedures used in Example 6 were performed to obtain a non-crimped staple fiber, except that the fiber was cut with a draft rate of 0.98 between the rotary cutter and the feed rollers. The evaluation results for the meta-type wholly aromatic polyamide non-crimped staple fiber are presented in Table 4.

TABLE 4 Unit Com. Ex. 4 Com. Ex. 5 Com. Ex. 6 Fiber configuration — Single component Single component Single component fiber fiber fiber Organic resin — meta-type Wholly meta-type Wholly meta-type Wholly aromatic polyamide aromatic polyamide aromatic polyamide Cutting method — Guillotine Guillotine Rotary cutter Fineness dtex 0.80 0.80 0.80 Fiber length mm 3.0 1.0 3.0 Moisture content weight % 15 15 15 Cut-end coefficient — 1.60 1.80 1.08 coefficient of variation % 33.0 60.0 17.0 relative to fiber length Water dispersibility — Poor Poor Acceptable

Example 9

High-density polyethylene (HDPE) with an MFR of 20 g/10 min and a melting point Tm of 131° C. was selected as a low-melting-point thermal binder component, and isotactic polypropylene (PP) with an MFR of 39 g/10 min and a Tm of 160° C. was selected as a fiber forming component. These polyolefins were separately melted with different extruders, and melt ejected through a concentric core-sheath conjugate spinneret having 1336 round ejection holes. The polymers were ejected as a conjugate of 245° C. molten polymers with a composition containing an HDPE sheath component and a PP core component in a sheath-to-core ratio of 50:50 (weight ratio). Here, the polymers were melt ejected at a rate of 190 g/min with a spinneret temperature of 260° C. The ejected polymer was cooled with 27° C. cool air at a position 31 mm below the spinneret, and a polyether•polyester copolymer emulsion was imparted to the yarns with an oiling roller. The fiber was then taken up at 1300 m/min to obtain an undrawn yarn. The undrawn yarn was bundled, and drawn 4.10 times in 95° C. hot water. After imparting a polyether•polyester copolymer as draw oil, the fiber was dried at 105° C. for 60 min to obtain a polyethylene/polypropylene conjugate fiber bundle having a single yarn fineness of 0.32 decitex, and a total fineness of 70000 denier. After imparting water to the conjugate fiber bundle with an oiling roller to make the moisture content 15%, the fibers were cut into staple fibers with a fiber length of 3.0 millimeters, using an Eastman rotary cutter fiber cutting device with a blade interval of 3.0 millimeters. The fiber bundle was cut with a draft rate of 1.02 between the rotary cutter and feed rollers under the pressure of a pressure roller pressing the fiber bundle against the cutter blade. Table 3 shows the evaluation results, including the fineness, the moisture content, the cut-end coefficient, the coefficient of variation relative to fiber length, and the water dispersibility of the polyolefin non-crimped conjugate staple fiber.

Example 10

Isotactic polypropylene (PP) with an MFR of 39 g/10 min and a melting point Tm of 160° C. was selected as an organic resin for forming a staple fiber. The isotactic polypropylene was melted with an extruder, and melt ejected as a 255° C. molten polymer using a spinneret having 3000 round ejection holes. Here, the polymer was ejected at a rate of 190 g/min with a spinneret temperature of 260° C. The ejected polymer was cooled with 27° C. cool air at a position 25 mm below the spinneret, and taken up at 1300 m/min to obtain an undrawn yarn. The undrawn yarn was bundled, and drawn 2.70 times in 95° C. hot water. After imparting a polyether-polyester copolymer as draw oil, the drawn yarn was dried at 110° C. for 60 min to obtain a polypropylene fiber bundle having a single yarn fineness of 0.30 decitex, and a total fineness of 70000 denier. After imparting water to the polypropylene fiber bundle with an oiling roller to make the moisture content 15%, the fibers were cut into staple fibers with a fiber length of 3.0 millimeters, using an Eastman rotary cutter fiber cutting device with a blade interval of 3.0 millimeters. The fibers were cut with a draft rate of 1.02 between the rotary cutter and feed rollers under the pressure of a pressure roller pressing the fiber bundle against the cutter blade. Table 5 shows the evaluation results for the polypropylene non-crimped staple fiber.

Example 11

High-density polyethylene (HDPE) with an MFR of 20 g/10 min and a melting point Tm of 131° C. was selected as an organic resin for forming a staple fiber. The high-density polyethylene was melted with an extruder, and melt ejected as a 210° C. molten polymer using a spinneret having 144 round ejection holes. Here, the polymer was ejected at a rate of 15 g/min with a spinneret temperature of 210° C. The ejected polymer was cooled with 27° C. cool air at a position 25 mm below the spinneret, and taken up at 1000 m/min to obtain an undrawn yarn. The undrawn yarn was bundled, and drawn 3.60 times in 95° C. hot water. After imparting a polyether-polyester copolymer as draw oil, the drawn yarn was dried at 105° C. for 60 min to obtain a polyethylene fiber bundle having a single yarn fineness of 0.32 decitex, and a total fineness of 70000 denier. After imparting water to the polyethylene fiber bundle with an oiling roller to make the moisture content 15%, the fibers were cut into staple fibers with a fiber length of 3.0 millimeters, using an Eastman rotary cutter fiber cutting device with a blade interval of 3.0 millimeters. The fibers were cut with a draft rate of 1.02 between the rotary cutter and feed rollers under the pressure of a pressure roller pressing the fiber bundle against the cutter blade. Table 5 shows the evaluation results for the polyethylene non-crimped staple fiber.

TABLE 5 Unit Ex. 9 Ex. 10 Ex. 11 Fiber configuration — Sheath-core conjugate Single Single fiber component fiber component fiber Organic resin — Core component: PP, PP HDPE Sheath component: PE Cutting method — Rotary cutter Rotary cutter Rotary cutter Fineness dtex 0.32 0.30 0.32 Fiber length mm 3.0 3.0 3.0 Moisture content weight % 15 15 15 Cut-end coefficient — 1.03 1.03 1.04 coefficient of variation % 3.8 4.5 4.8 relative to fiber length Water dispersibility — Good Good Good

Comparative Example 7

Twenty of the non-crimped polypropylene/polyethylene sheath-core conjugate fiber bundles obtained after imparting water in the manner described in Example 9 were bundled to obtain a fiber bundle of 1400000 decitex. The fiber bundle was then wrapped in paper. The wrapped sheath-core conjugate fiber bundle was cut into a fiber length of 3.0 millimeters to obtain a non-crimped staple fiber, using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The evaluation results for the polypropylene/polyethylene sheath-core conjugate staple fiber are presented in Table 6.

Comparative Example 8

Twenty of the polypropylene fiber bundles obtained after imparting water in the manner described in Example 10 were bundled to obtain a fiber bundle of 1400000 decitex. The fiber bundle was then wrapped in paper. The wrapped polypropylene fiber bundle was cut into a fiber length of 3.0 millimeters to obtain a non-crimped staple fiber, using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The evaluation results for the polypropylene non-crimped staple fiber are presented in Table 6.

Comparative Example 9

Twenty of the polyethylene fiber bundles obtained after imparting water in the manner described in Example 11 were bundled to obtain a fiber bundle of 1400000 decitex. The fiber bundle was then wrapped in paper. The wrapped polyethylene fiber bundle was cut into a fiber length of 3.0 millimeters to obtain a non-crimped staple fiber, using a known guillotine fiber-bundle cutter device (Onouchi Seisakusho, Model: D100) that had been adjusted to make this fiber length. The evaluation results for the polyethylene non-crimped staple fiber are presented in Table 6.

TABLE 6 Unit Com. Ex. 7 Com. Ex. 8 Com. Ex. 9 Fiber configuration — Sheath-core conjugate Single Single fiber component fiber component fiber Organic resin — Core component: PP, PP HDPE Sheath component: PE Cutting method — Guillotine Guillotine Guillotine Fineness dtex 0.32 0.30 0.32 Fiber length mm 3.0 3.0 3.0 Moisture content weight % 15 15 15 Cut-end coefficient — 1.50 1.60 1.60 coefficient of variation % 50.0 70.0 75.0 relative to fiber length Water dispersibility — Poor Poor Poor

Comparative Example 10

The same procedures used in Example 9 were performed to obtain a non-crimped staple fiber, except that the fibers were cut at a draft rate of 0.98 between the rotary cutter and the feed rollers. The evaluation results for the polyethylene/polypropylene sheath-core conjugate non-crimped staple fiber are presented in Table 7.

Comparative Example 11

The same procedures used in Example 10 were performed to obtain a non-crimped staple fiber, except that the fibers were cut at a draft rate of 0.98 between the rotary cutter and the feed rollers. The evaluation results for the polypropylene non-crimped staple fiber are presented in Table 7.

Comparative Example 12

The same procedures used in Example 1 were performed to obtain a non-crimped staple fiber, except that water was sprayed to make the moisture content 1.0% before being supplied to the rotary cutter to be cut. The evaluation results for the polyester non-crimped staple fiber are presented in Table 7.

TABLE 7 Unit Com. Ex. 10 Com. Ex. 11 Com. Ex. 12 Fiber configuration — Sheath-core conjugate Single Single fiber component fiber component fiber Organic resin — Core component: PP, PP PET Sheath component: PE Cutting method — Rotary cutter Rotary cutter Rotary cutter Fineness dtex 0.32 0.30 0.51 Fiber length mm 3.0 3.0 3.0 Moisture content weight % 15 15 1.0 Cut-end coefficient — 1.04 1.05 1.15 coefficient of variation % 25.0 32.0 25.0 relative to fiber length Water dispersibility — Poor Poor Poor 

1-4. (canceled)
 5. An organic resin non-crimped staple fiber for wet-laid nonwoven fabrics, the organic resin non-crimped staple fiber having a fineness of 0.0001 to 0.6 decitex, a fiber length of 1.0 to 5.0 millimeters, a moisture content of 10 to 100 weight %, a cut-end coefficient of 1.00 to 1.40, and a coefficient of variation relative to fiber length (CV %) of 0.0 to 15.0%, the cut-end coefficient, and the coefficient of variation relative to fiber length being defined as follows: Cut-End Coefficient=b/a,  (1) wherein a is the fiber diameter of a single yarn of the non-crimped staple fiber, and b is the maximum diameter at the cut end; Coefficient of Variation Relative to Fiber Length(CV %)=(standard deviation of fiber length)/(mean value of fiber length)×100(%),  (2) wherein the number of measured single yarns is 50 in (1) and (2).
 6. The organic resin non-crimped staple fiber according to claim 5, wherein the non-crimped staple fiber is a polyester non-crimped staple fiber, a wholly aromatic polyamide non-crimped staple fiber, or a polyolefin non-crimped staple fiber.
 7. The organic resin non-crimped staple fiber according to claim 5, wherein the non-crimped staple fiber is a polyethylene terephthalate non-crimped staple fiber, a polytrimethylene terephthalate non-crimped staple fiber, a polytetramethylene terephthalate non-crimped staple fiber, a polyethylene naphthalate non-crimped staple fiber, a polytrimethylene naphthalate non-crimped staple fiber, a polytetramethylene naphthalate non-crimped staple fiber, a meta-type wholly aromatic polyamide non-crimped staple fiber, a para-type wholly aromatic polyamide non-crimped staple fiber, a polyethylene non-crimped staple fiber, or a polypropylene non-crimped staple fiber.
 8. The organic resin non-crimped staple fiber according to claim 5, wherein the non-crimped staple fiber is a conjugate fiber configured from two or more organic resins.
 9. The organic resin non-crimped staple fiber according to claim 6, wherein the non-crimped staple fiber is a polyethylene terephthalate non-crimped staple fiber, a polytrimethylene terephthalate non-crimped staple fiber, a polytetramethylene terephthalate non-crimped staple fiber, a polyethylene naphthalate non-crimped staple fiber, a polytrimethylene naphthalate non-crimped staple fiber, a polytetramethylene naphthalate non-crimped staple fiber, a meta-type wholly aromatic polyamide non-crimped staple fiber, a para-type wholly aromatic polyamide non-crimped staple fiber, a polyethylene non-crimped staple fiber, or a polypropylene non-crimped staple fiber. 